CONFIDENTIAL

UNIVERSITI TUN HUSSEIN ONN MALAYSIA

FINAL EXAMINATION-ANSWER SCHEMESSEMESTER I

SESSION 2012/2013

COURSE NAME : FOUNDATION ENGINEERING

COURSE CODE : BFC 4043/43103

PROGRAMME : 4 BFF

EXAMINATION DATE : JANUARY 2013

DURATION : 3 HOURS

INSTRUCTION : ANSWER ALL QUESTIONS IN SECTION A AND THREE (3) QUESTIONS IN SECTION B

THIS QUESTION PAPER CONSISTS OF FIFTEEN (15) PAGES

CONFIDENTIAL

BFC 4043/BFC 43103

Marks TotalQ1(a) Notes: in Das (2011) textbook, there are few methods were

described as mechanical and hydraulic modifications. The mechanical modification is namely (i) compaction; (ii) vibroflotation; (iii) blasting; (iv) precompression; and (v) dynamic compaction. And (i) sand drains; (ii) prefabricated vertical drains; (iii) stone columns; and (iv) sand compaction piles are the hydraulioc modfication types.

Since the marks are only THREE (3) for each types, I would reckon it would be a totally brief discussions.

MECHANICALCompactionPrimary improvement: primary effects in bearing capacity.Curing time days: 10 – 100 daysEquipment size: small and medium.Range of particle size: medium gravel to medium silt.

VibroflotationPrimary improvement: primary effects in bearing capacity.Curing time days: 10 – 100 days, or 100 – 1000 days.Equipment size: large.Range of particle size: medium gravel to medium silt.

BlastingPrimary improvement: primary effects in bearing capacity.Curing time days: 10 – 100 days.Equipment size: medium and large.Range of particle size: coarse sand to fine silt.

PrecompressionPrimary improvement: primary effects in bearing capacity.Curing time days: 100 – 1000 days.Equipment size: primary medium, secondary small.Range of particle size: coarse silt to medium clay.

Dynamic CompactionPrimary improvement: primary effects in bearing capacity.Curing time days: 10 – 100 days.Equipment size: large.Range of particle size: medium gravel to fine silt.

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HYDRAULICSand DrainsPrimary improvement: rate of consolidation.Curing time days: 1 – 10 days, or 10 – 100 days.Equipment size: small, or medium. Range of particle size: medium gravel to medium clay.

Prefabricated vertical drainsPrimary improvement: rate of consolidation.Curing time days: 1 – 10 days, or 10 – 100 days.Equipment size: small, or medium. Range of particle size: medium gravel to medium clay.

Stone columnsPrimary improvement: structural, some in mechanial.Curing time days: 1 – 10 days, some 10 – 100 days.Equipment size: large.Range of particle size: medium sand to medium clay.

Sand compaction pilesPrimary improvement: structural and mechanical.Curing time days: 1 – 10 days, some 10 – 100 days.Equipment size: medium, large.Range of particle size: medium gravel to medium clay.

(1) Mechanical effects: loading, pore pressure release, etc, (2) Bearing

capacity: includes also reduced compressibility, (6) Rate of

consolidation: where increasing the rate itself is the objective, (6)

Permeability: where an increase or decrease of permeability is the

objective, (7) Curing time: the time necessary for a major part of the

effect to develop, (7) Small equipment: equipment that can be lifted by a

normal building crane, (8) Medium equipment: ordinary self moving

construction equipment accessible at most sites, (9)Large equipment:

very large or highly specialized equipment.

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Q1(b) 1/2

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Q1(c) The primary consolidation settlement of the clay layer caused by the addition of the permanent load, ’(p):

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The time required for 80 % of primary consolidation settlement under the addition permanent load only:If U = 80%, Tv = 0.567.

The temporary surcharge, ’(f), that will be required to eliminate the entire primary consolidation settlement in 12 months by the precompression technique:

For U% > 60%;

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Q2 Marks TotalQ2(a)(i) Plate bearing test is performed for the determination of

bearing capacity of soils for allowable settlement under static loads at shallow foundation.

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Q2(a)(ii)

Standard Penetration Test (SPT), Vane Shear Test (VST) and Pressuremeter Test (PMT).

These tests require boreholes because;the measurement can be taken at desired depth to get an accurate result;

the devise can be installed easily i.e., PMT;

can be used together with other drilling method and readily available equipment such as conduct SPT and VST test using wash boring method.

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Q2(a)(iii)

Refer to figure, the pressure at 15 m depth is Po = 100 + 18(5) +(22-9.81)(10) = 311.9 kN

So, CN =

Ncorrected = 30(0.607) = 18

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Q2(b)(i)

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The wall thickness =

When samples are to be taken in very stiff to hard clay mixed with stones, sampling tubes with high area ratio are required.

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Q2(b)(ii)

A bucket auger is not suitable to be used for soft clay soil. This method is used in suitable condition such as firm and dense soils or soft rocks. It may not be possible in very soft clay or coarse sand because the hole tends to collapse when auger is removed.

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Q2(b)(iii)

Testing for undisturbed sample – shear strength, consolidation, permeability.

Testing for disturbed sample – particle size distribution, specific gravity, Atterberg limit, moisture content, compaction.

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Q3 Marks TotalQ3(a) Soil: medium dense to dense sand , Ø = 34° , γ sat = 19

kN/m3, c = 0 kPaSoil below groundwater table is fully saturated and submerged , γ ‘ = 19 – 9.81 = 9.19 kN/m3

Soil above groundwater table is assumed to be saturated but not submergedDepth of footing: Df = 1 m Depth of groundwater table is 1 m from ground surfaceLoad to be carried by footing: Q all = 2000 kNFactor of safety ( FS) = 2.5

For c = 0 kPa;

from provided Meyerhoff’s table;with

shape factor:

depth factor:

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for > 0 as for = 34 and = 0.67

load inclination factor, since load is vertical

then, by merging all the data:

Therefore, the size of the footing and bearing capacity of the soil are not adequate to carry the load of 2000 kN.

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Q3(b)

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Q3(c) Since foundations are frequently covered or completely buried soon after their construction, there is limited opportunity for noting and correcting improper work or detecting conditions not in accord with design assumptions.

To minimize the risk of problems resulting from improper or inadequate foundation construction, the practice of having such work guided (or supervised) by personnel with soil mechanics (geotechnical) training is essential.

The responsibilities of such personnel would include matching soil and groundwater conditions observed in excavations with the conditions indicated by the borings used for design.

For projects where shallow foundations are being installed, the proper location, size and depth should be verified.

The bottoms of excavations should be examined prior to concrete placement to ensure that disturbed or muddy soil is not left in place; compaction or removal can be ordered if such conditions are observed.

Personnel doing supervision work should keep a written record( daily logs or reports) of activities, observations, and decisions regarding the foundation work.Copies frequently are expected to be forwarded to the designer’s office.

Written records can serve as a diary of the construction progress, and frequently serve as a reference if disputes develop.

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Q4 Marks TotalQ4 The proposed answers may vary with our student answers. Since the solutions

can be fairly subjective (several different assumptions may end up with different result too).Therefore, these answer schemes may be considered as a guideline for you. It’s up to you to decide on any other parameters.

Q4(a)(i)

Pile group efficiency

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For most practical purposes, the ultimate load of pile group, , can be estimated based on the smaller value of the

following two values [Figures (a) and (b)]:

Group Action – block failure (Figure (a)) of pile group by breaking into the ground along an imaginary perimeter and bearing at the base. The ultimate capacity for the group failure can be estimated from the following relationship:

Individual Action (Figure A) – if there is no group action (when the center to center spacing, s, is large enough, >1), in that case, the piles will behave as individual piles. The total load of the group can be taken as n times the load of the single pile.

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Q4(a)(ii)

Bearing capacity of pile resting on rockGoodman (1980) has approximate the ultimate unit point resistance in rock as , where

; qu = unconfined compression strength of rock, and - drained angle of friction;

after taking care of scale effect, ; and

the allowable point bearing capacity, Qp is

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Q4(a)(iii)

Small displacement In general, it is a steel pile; Examples of these piles are rolled steel section,

screw piles or open ended tubes and hollow section where the soil is removed during

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penetration. Rolled steel section piles are easily handled and

can be driven hard. They can be driven in very long lengths and the pile length can be readily varied.

Screw piles are valuable in marine works because they can resist both tensile and compressive forces.

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Q4(b)(i)

Lg group

Bg group

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Q4(b)(ii)

Step 1: the consolidation cut-off lineThe consolidation is from 2/3 of the pile length (from surface). Total pile length= 8.5m. Therefore:2/3 (8.5m) = 5.7 m from surface.

Therefore, the consolidation process will involve 2 layers. 0.8m for the first clay layer & 5m thickness of the second clay layer. It’ll be great if the student show the free body diagram.

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Step 2: the settlement at the first layer (0.8 m clay)

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Step 3: the settlement at the second layer (5 m clay)

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Step 4: total settlement for all layers= first layer + second layer= 84 + 142= 226 mm

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Q5 Marks TotalQ5(a) In any retaining structures resting on soft soil (loose sand,

soft clay ) there is possibility of the soil which close to dredge line will move upward or heave. This phenomena should be controlled by SF against heave at the lowest point of ret structure using the following formula :SF heave = M resisting / M driving

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Q5(b)

Every retaining structures will experience horizontal deformation, this should be controlled. The formulation to control horizontal deformation is using the chart made by Clough et. al. (1989)

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Q5(c) Free earth support determines the point of simple support position at the lowest point of sheet pile, whereas fixed earth support at certain length below dredge line depends on soil condition below dredge line. Free earth support needs Moment reduction whereas the other doesn’t.

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Q5(d)(i)

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Q5(d)(ii)

z (m) o’ = H a Lr (m) Le (m) L (m)

1.5 27 7.29 3.9 15.8 19.73 54 15.12 3.65 16.4 20.1

4.5 81 22.41 2.86 16.2 19.16 108 3.70 2.08 2.1 4.2

7.5 135 10.99 1.30 4.8 6.19 164 18.28 0.52 6.5 7.010 180 23.14 0 7.5 7.5

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